The oil shaped charges have been widely used in the oil and natural gas industry for many years. Oil and natural gas flow into the wellbore through perforations in the cased wellbore as the perforations are usually performed using a perforating gun loaded with shaped charges.
In general, an oil shaped charge is made of a case, a liner and explosive. The case is mostly made of steel, zinc, aluminum, copper, ceramics, etc. The liner is composed of a few powder metals or solid metals. To increase penetrating capability, tungsten powder, which density is 19.3 gram/cm3, is used as the main component in the mixed metal powder. Since the tungsten powder is a brittle-like metal material, copper powder is added to the mixed powder as an adhesive. After initiation of the shaped charge through an access hole, an explosive shock wave propagates toward into the inside explosive layer. Since the shock wave is compact with highly pressure, the liner is collapsed and forms a high speed jet so the high speed jet can penetrate a perforating gun and a casing. Then the high speed jet continuously penetrates into the rock layer where oil or natural gas is reserved.
The penetrating depth of the high speed jet in a rock layer depends on tip speed, and total effective length of the jet. The definition of the effective jet length is given by (Vtip−Vrear)×t, where Vtip, Vrear and t are the tip speed, rear speed and time, respectively. Since the high speed jet is mostly made of metal powder, if the tip speed is too high, it disperses and therefore loses penetration capability. For the oil shaped charges, maximum speed can reach as high as 8000 m/sec or even higher, but usually the tip speed of a traditional oil shaped charge is in the range of 5500 m/sec through 6500 m/sec. Tests have shown that a high speed jet with the speed of 600 m/s can still penetrate a concrete target with strength greater than 5500 psi. However, for most of oil shaped charges, the rear speed is in the range of 1100 m/sec through 1300 m/sec. The X-ray tests show that after 1100 m/s, the rear of the high speed jets disperse and lose penetrating capability. In a traditional shaped charge, the effective length of the liner material is only one half of the liner total length and the effective explosive is also around half of the total weight. Additionally, the traditional shaped charge designs create large reverse tip velocity which wastes a lot of liner material and explosive. As a result, the total length of the high speed jet is relatively short and the penetrating capability is low.
It is therefore an objective of the present invention to provide a shaped charge design for super penetration by changing the configurations of the liner and the proper placement of the explosive material. For example, when the effective liner material and explosive are increased, the effective kinetic energy of the jet increases, which in turn increases penetration. The unique outer wall configuration of the linear and the unique inner wall configuration of the case allow the explosive material to be effectively placed in between the linear and case so that the maximum penetration can be achieved by the high speed jet.